People keep going on about the chickens. The reality is that many people eat a lot more than the recommended portions of meat.
A normal medium chicken is about 1.8 kg, about half that will be meat, the rest bones etc. If you serve your roast dinner with stuffing, roast potatoes and other vegetables, 2 breasts between 4 people is ample.
You then take the meat off the legs and use these in a pie, risotto, curry, tagine, etc etc etc - put vegetables in the meal and again, this will do 4 people a full meal.
You will then have the carcass with scraps of meat on it including the oysters and quite a lot of other meat on the back and any other bits still stuck to the carcass.
If you boil this to make stock and use the stock in something like a noodle soup with the bits of chicken and other vegetables that is how you make a chicken do three meals for 4 people. Instead of a noodle soup, you could add pearl barley and carrots/onions/swede to make a broth.
This is how it should be and making fewer meals than that is being a bit greedy really.
It's also important to note the types of things that people with smaller than average shopping budgets don't buy. They probably don't use Waitrose or Ocado, they probably cook from scratch a lot more than eating ready prepared food.
They probably use more traditional cooking methods where meat is a smaller, but still satisfactory, part of the meal, accompanied by seasonal vegetables and pulses, as described above, or use cheaper cuts of meat like pork shoulder rather than steaks or lamb.
They will shop around and stock up on things on offer, rather than just buying what they need, as they need it from the same supermarket every week.
They probably don't buy much in the way of fresh fish, organic meat, fresh berries or other imported fruit, prepared fruit and vegetables, fresh juices and smoothies. Things like berries and fish can be bought frozen for less than half the cost of fresh.
Just the difference between picking whatever you fancy from expensive supermarkets like Waitrose and buying just what you need from Aldi can reduce the weekly bill by more than half.